Engine Tries to Crank but Won't Turn Over

[MikeB1970]

I've got a 1970 F100 with a 302 5.0 V8. Everything is stock OEM / aftermarket parts "standard" parts - no mods. Recently she's become a little hard to crank, but has eventually fired up. Now, it sounds normal when I turn the key, but once I let go of the key nothing happens - it just dies. My neighbor came over and put a voltmeter on it, and according to him I've got power when I'm turning the key but then there's no power after I let go of the key. He's a mechanic at his job, but bigger stuff than old 302 truck engines (not really an auto mechanic), and he says I've got fuel and spark, so there's something else causing the problem. Anybody got a suggestion? Video is located at: https://www.youtube.com/watch?v=bleVnaE ... e=youtu.be[/video]

[HIO Silver]

Do you have 12Vdc at the "I" terminal of the starter solenoid with the ignition "on"?

[sargentrs]

You can also run a jumper wire from the battery + to the coil + and try to start it. If it runs you'll know it's the ignition circuit. Pull the jumper wire to kill it.

[69Ford]

See if you have voltage to the coil with the key in the run position should be around 9 volts if it is a points system. If I am correct the truck starts in start position but stalls as soon as you release the ignition switch to the run position. To me this could be a bad ignition switch or the resister wire from the switch to the coil fried. When the key is in the start position it bypasses the resister wire to put a full 12 volt to the coil that is why it will run in this position. Hopefully this makes some sense. Should be real simple to track down with a voltmeter.

[fordman]

Bad old worn out ignition switch.

[69Ford]

Not an expert on fuel delivery but maybe your fuel pumps bad. Just enough fumes in the carb to run a few seconds. If you do find the culprit let us know. Thanks

[MikeB1970]

Sorry for the slow reply - lots of rain kept me out of the driveway and out from under the hood of the old girl, Anyway, thanks for all the suggestions. I tested everything with the multi-meter and the culprit seemed to be the solenoid although it wasn't real clear-cut (the readings were not quite what everything on the internet said i should be seeing). I replaced it anyway and I have been rewarded with the satisfying roar of the 302 coming to life then purring contentedly like she should. Kudos to my 12-year old daughter for being my assistant in the cab while I was playing with the multi-meter.